This invention relates to methods and apparatus for testing electronic devices, and more particularly, to electronic device testers that automatically change force conditions and measurement settings on the fly in the course of a test sequence, without system controller intervention.
When testing electronic devices such as voltage regulators and other circuits, it is desirable to test the devices under a variety of test conditions. When testing voltage regulators, for example, it is desirable to apply or force a series of different input voltages to the voltage regulator under test, and/or load the devices to produce a variety of forced output currents, and measure the output voltage to determine whether the device performs within specifications. Input parameters can also be measured, if desired. For example, if a constant input voltage is provided to the device, the input current can be measured as a test of device performance. In any event, it is desirable to test not only steady state device performance, but performance under transient conditions, as well. Of course, the entire series of tests must be performed as quickly as possible, preferably in an automated manner.
Known apparatus for testing electronic devices automatically performs a sequence of tests by forcing different inputs to devices under test and measuring various responses from those inputs. A computer initiates the test sequence and changes various measurement parameters during the test sequence, using processor driven software in the computer. The computer typically controls a plurality of test apparatus.
An example of such apparatus is shown in FIG. 7. In FIG. 7, a device under test (DUT) 10, shown as a resistive load, has two terminals 12, 14 for connection to test apparatus 16. The test apparatus 16 is controlled by a system controller 18, such as a personal computer or the like. Clock signals 20 are provided to synchronize the test apparatus 16 with other test apparatus in the system (not shown) through a system clock controller 21.
The test apparatus 16 includes an arbitrary waveform generator (AWG) RAM 22. The AWG RAM 22 generates data representing a series of conditions under which the DUT 10 is tested. The data is converted to a desired analog waveform in a digital to analog converter (DAC) 24. The DAC 24 produces the test conditions as forced inputs that pass through an output stage 26 and a current monitor and range switching circuit 28 to the DUT 10. The forced input to the DUT 10 can be a voltage or a current that changes in amplitude perhaps many times during a test sequence.
The voltage response of the DUT 10 to the test conditions is sensed by a differential amplifier 30. In FIG. 7, the differential amplifier 30 measures the voltage across the DUT 10 when the forced input is applied, and the current monitor and range switching circuit 28 senses the current drawn by the DUT 10. The measurements are provided to an analog-to-digital converter/digitizer (ADC) 32. The digital data produced by the ADC 32 is provided to the system controller 18, which processes the test data gathered through the entire test sequence, and determines whether the DUT 10 meets the test specifications for the device.
The waveform data generated by the AWG RAM 22 to create the forced input is produced as a Random Access Memory (RAM) controller 34 counts through a predetermined number of steps under the control of the system clock signal 20. The RAM controller 34 generates addressing information for the AWG RAM 22. The RAM controller 34 is initially loaded with a start address from the system controller 18, and automatically increments the AWG RAM addresses on the fly, without intervention by processor driven software in the system controller 18.
In this known apparatus, test equipment measurement settings are made by the system controller 18, using processor-driven software. Changing test equipment settings in this manner is relatively slow and time consuming, particularly if one system controller is shared by several test apparatus set-ups. Since several setting changes might be needed within a single test sequence, this processing increases the time required for testing the device.
Another feature of the known apparatus is the operation and accumulation of data in the ADC 32. For example, the ADC 32 operates continuously whenever system clock signals 20 are provided, so a good deal of unneeded data is generated and must be processed which is time-consuming. Also, multiple test readings are sometimes stored in the ADC 32 and transferred to the system controller in blocks for processing. This process further slows the test sequence due to the time required for data transfer, which also increases the time required for testing the device.
Accordingly, one object of this invention is to provide new and improved apparatus for testing electronic devices.
Another object is to provide new and improved electronic device testers that reduce the time required for testing.
In keeping with one aspect of the invention, apparatus for testing an electronic device under a plurality of test conditions created during a test sequence includes an arbitrary waveform generator that sequentially generates various forced voltage or forced current waveforms. The arbitrary waveform generator is controlled by data stored in an associated memory. The memory also includes data that selects a forced voltage mode or a forced current mode for the generator, and can change the maximum current producing capability or current range of the generator.
One or more measuring devices store a plurality of results during the test sequence using a series of range and other settings. The settings of the measuring devices are selected and set using data stored in memory, preferably the memory used by the arbitrary waveform generator.
A controller initiates the test sequence and determines whether measured results are within predetermined specifications. The controller uses processor-driven software, but the settings of the measuring devices and/or the maximum current range of the generator are changed at predetermined times during the test sequence, without using the controller""s processor-driven software. It is contemplated that not all settings need be changed without controller intervention, to practice the invention. The data can also be used to turn the measuring devices on and off during the test sequence, if desired, in a similar manner.
In another aspect of the invention, at least one of the measuring devices makes sets of sample measurements over a period of time. The samples are added independently of the controller, and the controller divides the total by the number of samples taken, to calculate the average result.